Polyphenols are thermosetting and their cured formulation exhibit excellent physical characteristics and heat resistance, thus polyphenols are regarded as important industrial materials, which are utilized to molding materials, raw materials for inks, paints, varnishes, adhesives, etc., raw materials for epoxy resins, curing agents, etc. By taking advantage of their characteristically high electrical insulation properties, polyphenols also exhibit remarkable electrical insulating properties, so that they have been favorably used for composite electronic materials such as printed circuit boards, semiconductor encapsulating materials, inks, paints, varnishes, and adhesives as materials of the electronic field.
In those fields where polyphenols are applied, high fire retardancy should be required. For example, materials obtained by adding 10 to 50 weight parts of a fire retardant additive, such as a brominated epoxy resin, to 100 weight parts of a polyphenol resin are in use. However, some of such halogen-containing compounds generate toxic halogen gases on incineration and the burdens and ill effects on the environment and human physiology are seriously concerned in case of incineration of used or waste products or thermal recycling by recovery of heat.
For this reason, as a fire retardation technology without using halogen-containing compounds, materials containing phosphorus-compounds are being explored. But some of such fire retardant additives detract from the mechanical properties and moisture resistance of shaped articles, not to speak of the risk for the eutrophication of the soil or natural water by phosphorus-containing pollutants from discarded products and waste materials. It is urgently needed to develop a novel fire retardation technology completely different from the concept of using a phosphorus compound, which will be halogen-free and providing for not only good fire retardancy which are required of the molding materials for electronic use, adhesives, paints and the like, but also the favorable mechanical and electrical characteristics.
Referring to the prior art, Japanese Kokai Publication Hei-9-216938 discloses a method of producing a phenolic resin-cured epoxy resin which comprises subjecting a silicon alkoxide to hydrolysis and polycondensation in a solution of a phenolic resin consisting of such a structure that aromatic units having phenolic hydroxyl groups are connected to one another through a methylene group containing one carbon atom, and using the resulting phenolic resin-silica complex as a curing agent, mixing with an epoxy resin to cure. However, since said phenolic resin-silica complex for use as the curing agent does not provide for sufficient fire retardancy, the phenolic resin-cured epoxy resin produced by this method does not have sufficient fire retardancy to replace the materials produced by using said brominated epoxy resin, said phosphorus compound or other fire retardant additive. Thus, further technical sophistication was deeply desired in this respect.
Japanese Kokai Publication Hei-11-92623 discloses a method of producing a phenolic resin-silica complex which comprises subjecting a silicon alkoxide to hydrolysis and polycondensation in a molten phenolic resin. However, this complex cannot contribute to expression of sufficient fire retardancy, either, with the result that further technical sophistication should be developed to provide polyphenol compounds with fire retardancy as good as enabling production of halogen-free compositions.
Meanwhile, as a fire retardation technology, Japanese Kokai Publication Hei-10-36686 discloses that a resin composition comprising a resin and the condensation product of a defined metal alkoxide as main components has certain favorable characteristics such as heat resistance. However, further technical sophistication must be also studied to impart sufficient fire retardancy to electronic materials, for instance. Furthermore, Japanese Kokai Publication 2000-313614 discloses a technology relating to the hydrothermal treatment of the amorphous silica having a surface area smaller than 30 m2/g and a unimodal pore diameter distribution within the size range of 30 to 2,500 nanometers, and as estimated by the nuclear magnetic resonance signal, containing at least 10% of Q3 silanols and less than 0.5% of Q2 silanols. However, these amorphous silica must be also more improved to provide sufficient fire retardancy. Moreover, the preparation of hydrothermally-treated silica samples in the best mode invariably involve an alkali treatment and, therefore, some technological innovation is also needed to apply this technology without any problems in the field of electronic and other materials where liabilities are affected by alkalies. Furthermore, Japanese Kokai Publication Hei-9-208839 discloses a thermosetting resin composition comprising (A) a thermosetting resin, (B) an organopolysiloxane having functional groups reactive with silanol groups, (C) a silicon alkoxide, (D) a catalyst for the reaction of water with the silicon alkoxide, and (E) an organic solvent. However, even this thermosetting resin composition must be more improved in order that it may express sufficient fire retardancy with certainty.